Nodulation
Potassium humate
A perusal of data in Table 1 revealed that the application of potassium humate significantly increased nodulation parameters up to the treatment 4.5 kg/ha over control. Significantly maximum number of total nodules/plant, effective nodules/plant, fresh and dry weight of nodule (mg/plant), nodule index and leghaemoglobin content in nodule (mg/g) (37.89, 29.22, 137.60, 72.23, 1.27 and 2.02, respectively) were observed with the application of potassium humate @ 4.5 kg/ha followed by potassium humate @ 3 kg/ha over control. The lowest value of above parameters recorded under control. This effect might be due to presence of fulvic and humic acid in potassium humate. Humic acid supplies essential nutrients and minerals for plant growth, whereas the major function of fulvic acid is transport of nutrients. Potassium humate increased the availability of P in root zone, which in turn in better growth of root and shoot and also help in better nodulation
(Tripura et al., 2017). These findings were also supported by
Abdelhamid et al., (2011), Patil et al., (2011) and
Sarwar et al., (2014).
Fertility level
Significantly maximum number of nodules/plant, effective nodules/plant, fresh and dry weight of nodule (mg/plant), nodule index and leghaemoglobin content in nodule (mg/g) (37.83, 29.07, 139.35, 72.89, 1.27 and 1.97, respectively) were observed with application of 100% RDF followed by application of 75% RDF over control. This effect might be due to positive effects of nitrogen and phosphorus; Nitrogen provides favorable nutritional environment in the root zone for better growth of nodules. Phosphorus plays a major role in root development, improves root nodules and nitrogen fixation by roots. Plants receiving moderately high or high P had intermediate root length system and plant receiving high N concentration stimulated root growth and resulted in the longest root systems and nodulation
(Gentili et al., 2006). The present investigation is also conformity with
Suman et al., (2007), Singh and Sharma. (2011).
Interaction
The interaction effect of potassium humate and fertility levels on the total no. of effective nodules/plant and dry weight of nodule was significantly observed (Table 2 and 3). The treatment combination, potassium humate @ 4.5 kg/ha with 100% RDF (K
3F
3) recorded the maximum effective nodules/plant and dry weight of nodule (mg/plant) (33.98 and 84.02) which was remained at par on potassium humate @ 4.5 kg/ha with 75% RDF (K
3F
2) (32.28 and 80.26), potassium humate @ 3.0 kg/ha with 100% RDF (K
2F
3) (31.65 and 79.85), potassium humate @ 3.0 kg/ha with 75% RDF (K
2F
2) (31.43 and 78.57) over control (17.55 and 42.35). The significant increase in nodulation parameters under the application of potassium humate and fertility levels was largely function of improved root anatomy and soil health
(Idress et al., 2012). A synergistic interaction occurs between potassium humate and fertility levels
(Kumar et al., 2014) and resulted in increase in the fresh and dry weight of nodules. This finding was in agreement with
Abdelhamid et al., (2011), Ali et al., (2016).
Yield attributes and yield
Potassium humate
The data pertaining to the effect of potassium humate and fertility levels on yield attributes and yield of mungbean have been summarized in Table 4. Significantly maximum no. of pods/plant, no. of seeds/pod, test weight (g), seed and straw yield (kg/ha) (21.56, 8.95, 33.80, 1193 and 2617, respectively) was obtained with application of potassium humate @ 4.5 kg/ha followed by application of potassium humate @ 3 kg/ha over control. Humic acid improved plant net photosynthesis
via increasing chlorophyll and electron transport flux in plants, this leads to more transport of photosynthetic products from leaves and stem to grain indicating that higher the biomass at anthesis
(Aparicio et al., 2002). The results corroborated with the findings of
Sarwar et al., (2014), Taha and Osman (2018) and
Elkin et al., (2019).
Fertility levels
Significantly maximum no. of pods/plant, no. of seeds/pod, test weight (g), seed and straw yield (kg/ha) (22.07, 8.86, 34.47, 1197 and 2604, respectively) with application of 100% RDF followed by application of 75% RDF over control. Application of nitrogen in the early stage of mungbean is very important in promoting vegetative growth and biomass production. Hence, application of nitrogen stimulated seed setting and rapidly increased the yields attribute of mungbean
(Razzaque et al., 2017). Phosphorus plays an important role in energy transfer and conservation. During certain stage of development more assimilates are produced than used in development and growth of plant and excess assimilates are diverted in storage compounds. At later stage the storage compound remobilize and move to sink which increased the number of pods and seeds per pod
(Hernandez et al., 1983). These results were in recognizance with the findings of
Yakadri et al., (2002), Karwasra et al., (2006), Kumar (2015).
Interaction
The interaction effect of potassium humate and fertility levels on seed yield was significantly observed (Table 5). The treatment combination, potassium humate @ 4.5 kg/ha with 100 % RDF (K
3F
3) was recorded the maximum seed yield (1412.06 kg/ha) but it was found
at par with combined application of potassium humate @ 4.5 kg/ha and 75 % RDF (K
3F
2) (1347.84 kg/ha), application of potassium humate @ 3.0 kg/ha and 100% RDF (K
2F
3) (1343.32 kg/ha) and application of potassium humate @ 3.0 kg/ha and 75 % RDF (K
2F
2) (1310.25 kg/ha) over control. The significant increment in yields under the application of potassium humate and fertility levels was function of better growth and subsequent increment in yields. The synergistic interaction occurs between potassium humate and fertility levels had resulted in enhancement of number of pods per plant and seed per pods, ultimate the seed yield. This finding was in agreement with
Ali et al., (2016) and
Ranpariya et al., (2017).